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May 19, 1936- J. MAssoLLE ET AL Re. 19,974

ELECTRON TUBE Original 'File'd April 4, 1921 lNvENToRs g g JOSEPHMASSOLLE 6 l5 .4 .13 J2 I1 '0 l V0't HANS V067 BY Jos-F ENGL TToR'ZESReissued May 19, 1936 UNITED STATES ELECTRON TUBE Joseph Massolle,Gros-Glienicke, near Cladow,

Berlin,

Hans Vogt, Berlin-Dahlem, and Josef Engl, Berlin-Schmargendorf, Germany,assignors, by mesne assignments, to American Tri-Ergon Corporation, NewYork, N. Y., a corporation of New York Original No. 1,587,786, datedJune 8, 1926, Serial No. 458,635, April 4, 1921. Application for reissueApril 16, 1934, Serial No. 720,870.

Germany December 2, 1919 14 Claims.

The invention relates to electron tubes, particularly to thermionicamplifying tubes. The invention aims to improve the effectiveness inoperation of amplifier tubes, by overcoming an effect, or action, in theoperation of amplifiers of common type, which tends to reduce theamplications secured thereby. In the operation of the well-knownamplifier having an effective resistance in series with theplate-filament path of the tube, across the constant source of potential(B battery) of the tube, variation of input voltage causes a Variationin the plate-filament potential difference. With grid potentialincreasing from negative to less negative the plate current willincrease and the potential difference between plate and filamentdecreases. The operating conditions of the tube now correspond to adifferent current-Voltage curve; and a comparison of curves plotted fordifferent potentials at the plate will demonstrate that theamplification indicated by the second curve may be less than `thatindicated by the rst curve.

The effectiveness of the tube will, of course, be improved if acharacteristic curve of desirable steepness be selected, and if sucharrangements be provided that the operation will remain substantially onthe same curve, regardless of varying potential differences betweenplate and filament. The present invention provides means foraccomplishing this object, or, generally speaking, for reducing theeffect of variations in the plate potential in Varying the amplificationfactor of the tube. This is accomplished by the provision of anauxiliary anode, or anode screening member, preferably positionedbetween the plate or working anode and the grid, and connected to theconstant potential source of the tube, preferably in such manner thatthe potential difference between this screening member and the filamentis greater than that between the plate or working anode of the tube, andthe filament.

In order that the invention may be more clearly understood, attention ishereby called to the accompanying drawing, in whichz Figure 1 is adiagram giving a series of characteristic curves for a usual type ofamplifying tube, indicating the relations between grid potentials andplate current for varying plate potentials, the horizontal coordinate ofthe diagram indicating grid voltages and the vertical coordina teindicating plate current in milli-amperes, while the numerals at theleft hand side of the curves indicate the plate potentials of thevarious curves, in volts;

Fig. 2 is a View of an electron discharge tube (Cl. Z50-27) having ananode screening member, or auxiliary ande, in accordance with thepresent invention; an

Fig. 3 is a diagram of current voltage curvesl for the constructionshown in Fig. 2, the horizontal co-ordinate indicating grid voltages,and the vertical co-ordinate indicating plate current in milliamperes.

The curves shown in Figure 1 represent by way of example the relationsbetween grid potentials and plate current for varying plate potentials,recorded with ordinary amplifier tubes, the right hand curvecorresponding to 15 volts plate potential and the curves to the leftthereof successively 30, 40, 50, 60, and 90 volts. Below 40 volts, inthis example, the curves become less steep. It will be noted from thefigure that at zero grid voltage, for example, a plate current of about0.1 milliampere, is indicated at 30 volts plate potential, while at 40volts plate potential the plate current is about 0.25 milli-amperes.

It may be stated that one of the factors determining the plate currentis the influence of the plate acting through the openings of the grid,which may be considered as the passage of lines of force from the platethrough the grid. The characteristic curve described will be moved tothe left, into the range of negative grid potentials, as the passage oflines of force through the grid increases. This effect occurs if theplate potential be kept constant and the meshes of the grid areincreased in size, or if the meshes are kept the same size and thepotential at the plate is increased. Conversely, of course, thecharacteristic is shifted to the right proportionately as the potentialat the plate decreases.

To obtain high amplification it is desirable to operate within the rangeof negative potentials at the grid, as is well-known, a sufficientlynegative grid meaning a high resistance between filament and grid and arelatively high plate current. To attain this, the plate voltage must besuiciently high. In the example shown in Figure 1 the curves havemaximum steepness at plate voltages of 40 volts and upwards. It is,therefore, desirable to operate on curves of 40 volts plate potentialand upwards.

It will be noted that in the operation of three electrode amplifyingtubes of usual construction the working resistance outside the tube isconnected in series with the plate-filament path of the tube and withthe constant source (B-battery). If now, we assume, for example, thatthe grid potential becomes less negative momentarily because of changingconditions in the input circuit of the tube, the internal resistance ofthe tube between plate and filament then decreases and the plate circuitcurrent increases. The drop of potential across the external resistanceincreases and the potential drop within the tube between plate andfilament decreases. That is to say, the electrical conditions within thetube no longer correspond to the current-voltage curve which representedthem before the change in input potential, but to anothercurrent-voltage curve situated further to the right in a diagram such asthat of Figure l, in which case the amplification may not be so good.

In the construction shown in Fig. 2 illustrating the present invention,the input circuit is connected across the grid g and the filament lc asusual, variations in the input circuit causing a varying difference ofpotential eg across the grid and filament. The plate a2 is shown asconnected to the filament by an external connection which includes theresistance w and the source of steady plate current indicated as thebattery ea.

The anode screening member a is shown as connected to the positive poleof battery ea. Resistance w is included in the connection between platea2 and the positive pole of the battery, whereas this resistance is notincluded in the connection between the anode screen, or auxiliary plate,a' and the positive pole of the battery. Accordingly, this arrangementprovides for a greater drop of potential between the anode screen a' andthe filament, than exists between plate a2 and the filament because ofthe drop of the potential through resistance w. The outgoing circuit maybe considered as connected across the terminals of resistance w.

In the arrangement shown, which is preferred, the anode screen a islocated between grid g and plate a2. The potential supplied to anodescreen a by the battery or source ea is as nearly constant as possible.The effect of this screening or protecting electrode a is to greatlydecrease the electrostatic lines of force from the working anode orplate a2 through the openings of the grid. By decreasing this fluxthrough the grid to a minimum variation in the voltage of the plate willhave practically no effect in displacing the characteristic anodecurrent curve, and, accordingly, good amplification may be obtained,with plate voltage varying within considerable limits, the electricalcharacteristics of the tube being so chosen that a desirably positionedand sufficiently steep curve is made use of. Instead of having themember a interposed between the working plate and filament, it ispossible to have members a and a2 arranged one beside the other, thearrangement shown, however, being preferred.

In the example shown, the varying voltage of plate a2 has practically noinuence on the range or position of the current-voltage curve of thetube. This is demonstrated by the curves shown in Fig. 4 which wereobtained with a tube constructed according to the invention. A constantpotential of 90 volts was applied to the anode screen or auxiliary anodea' while voltages of 2O volts and volts respectively were applied to theworking anode or plate a2. It will be noted that both curves start fromthe same point on the horizontal co-ordinate and separate from eachother very slightly in the course of the upward rise of the curves,showing that the varying voltage of the plate, in this arrangement,exerts very little influence on the position of the curve.

The screening member a' is preferably grid-like or perforated in form.When this member has small meshes or openings therethrough and there isa relatively large distance between members a and a2, a proportionatelysmall number of electrons from the heated filament k will pass throughthe member a and reach plate a2. If, however, the meshes or the width ofthe openings in anode screen a are increased, or if the distance betweenmembers a and a2 is reduced, the number of electrons passing throughmember a to the plate a2 becomes relatively greater. As an extremeexample, the anode screen a may be reduced to consist of a single wireonly, in which case its surface becomes very small in comparison withthat of plate a2, and in that case a considerable part of the electronsemitted by the cathode will pass to plate a2.

It will be noted that as shown in the example in Fig. 2, the fullpotential of battery ea is applied constantly to the anode screen a',while the potential at plate a2 is reduced by the amount of thepotential drop across the resistance w. The potential of battery ea maybe divided, by means of a potentiometer or otherwise as desired toproduce other relations than those shown between the potentials atmembers a and a2, the only essential requirement, for best operation,being the fulfillment of the condition that the potential on plate a2must be less than that on the anode screen a.

We claim:-

1. In electron discharge tubes, the combination of a vacuous tube havingplate, grid and filament, and anode screening means located between saidplate and filament and having openings through which the plate currentpasses, an input circuit connected to the grid and filament, a source ofpotential, and connections therefrom to the plate, filament andscreening means, including greater resistance between said source andplate than between said source and screening means, so as to impose agreater potential difference between said screening means and filamentthan between said plate and filament, said tube having a positiveeffective internal resistance between plate and filament.

2. In electron discharge tubes, the combination of a vacuous tube havingplate, grid and filament, and anode screening means interposed betweenthe plate and grid and having openings through which the plate currentpasses, output terminals connected to said plate and filament, an inputcircuit connected to the grid and filament, a source of potential, andconnections therefrom to said output terminals and screening means,including an impedance in the connection from the positive terminal ofsaid source of potential to the output terminal of said plate, so as toimpose a greater potential difference between said screening means andlament than between said plate and filament, said tube having a positiveeffective internal resistance between plate and filament.

3. In electron discharge tubes, the combination of a vacuous tube havinganode, cathode and control electrode, and anode screening means locatedbetween said anode and cathode and having openings through which theplate current passes, means for impressing a varying potential acrossthe cathode and control electrode, a source of steady potentialconnected between the anode and cathode, a connection between thepositive side of said source and said anode screening means, and meansinterposed between said source and anode for reducing the potentialdifference between the anode and cathode due to said source to a valuebelow the potential difference between said anode screening means andsaid cathode, said tube having a positive eiective internal resistancebetween anode and cathode.

4. In electron discharge tubes, the combination of a vacuous tube havinganode, cathode and control electrode, and anode screening means, meansfor impressing a varying potential across the cathode and controlelectrode, said anode screening means being interposed between saidanode and control electrode and having openings through which the platecurrent passes, connections external to the tube between the anode andcathode, and means for imposing a potential difference between saidanode and cathode and a steady potential difference between said anodescreening means and said cathode greater than that between said anodeand cathode, said tube having a positive effective internal resistancebetween anode and cathode.

5. In electron discharge tubes, the combination of a vacuous tube havinganode, cathode and control electrode, and anode screening means locatedbetween said anode and cathode and having openings through which theplate current passes, means for impressing a varying potential acrossthe cathode and control electrode, external means for producing a steadypotential, and connections therefrom to said anode, cathode andscreening means so as to impose a greater potential difierence betweensaid screening means and cathode, than between said anode and cathode,said connections including an impedance providing for a drop ofpotential between said potential producing means and said anode, saidtube having a positive effective internal resistance between anode andcathode.

6. In electron discharge tubes, the combination of a vacuous tube havinganode, cathode and control electrode, and anode screening means, meansfor impressing a varying potential across the cath- 0de and controlelectrode, said anode screening means being interposed between saidanode and control electrode and having openings through which the platecurrent passes, connections external to the tube betwen the anode andcathode, a source of voltage for imposing a potential difference betweensaid anode and cathode and a steady potential difference between saidanode screening means and said cathode greater than that between saidanode and cathode, said tube having a positive eifective internalresistance between anode and cathode.

7. In electron discharge tubes, the combination of a vacuous tube havinganode, cathode and control electrode, and anode screening means, meansfor impressing a varying potential across the cathode and controlelectrode, said anode screening means being interposed between saidanode and control electrode and having openings through which the platecurrent passes, connections external to the tube between the anode andcathode, and a source of voltage for imposing a potential differencebetween said anode and cathode and a steady potential difference betweensaid anode screening means and said cathode greater than that betweensaid anode and cathode, said source of voltage being connected in serieswith the cathode-anode screening means path of said tube, saidconnections including a conductor for connecting said source of voltageas an entirety in series with the cathode-anode path of said tube, saidtube having a positive effective internal resistance between anode andcathode.

8. In electron discharge tubes, the combination of a vacuous tube havinganode, cathode and control electrode, and anode screening means, meansfor impressing a varying potential across the cathode and controlelectrode, said anode screening means being interposed between saidanode and control electrode and having openings through which the platecurrent passes, connections external to the tube between the anode andcathode, a source of voltage for imposing a potential diiference betweensaid anode and cathode and a steady potential difference between saidanode screening means and said cathode greater than that between saidanode and cathode, a conductor for connecting the positive terminal ofsaid source of voltage to said anode screening means, said connectionsincluding a conductor leading from said anode to said positive terminalof said source of voltage, and a resistance included in the circuit ofsaid last-named conductor, said tube having a positive effectiveinternal resistance between anode and cathode.

9. In electron discharge tubes, the combination of a vacuous tube havingplate, grid and filament, and anode screening means, said grid beinginterposed between said plate and lament and said anode screening meansbeing interposed between said grid and plate, said grid and anodescreening means having openings through which the plate current passes,an input circuit connected to the grid and filament, a source ofpotential, having its negative terminal connected to the lament, aresistance connected in series between the plate and the positiveterminal of the source, and a connection between said screening meansand a pointI between the positive pole of the source and the resistance,said tube having a positive effective internal resistance between plateand filament.

10. In electron discharge tubes, the combination of a vacuous tubehaving plate, grid and filament, and anode screening means interposedbetween said grid and plate and having openings through which the platecurrent passes, an input circuit connected to the grid and filament, asingle source of potential, having its negative terminal connected tothe filament, a resistance connected in series between the plate and thepositive terminal of the source, and a connection between said screeningmeans and a point between the positive pole of the source and theresistance, said tube having a positive elective internal resistancebetween plate and filament.

11. In combination: a multi-electrode electron discharge tube having acathode, a control grid, a screen grid and an anode, means applyingpositive potentials to the screen grid and anode relative to thecathode, and means maintaining said potential of the anode less positivethan that of the screen grid, said tube having a positive effectiveinternal resistance for voltage changes impressed between the controlgrid and the cathode.

12. In combination: a multi-electrode electron discharge tube having acathode, a control grid, a screen grid and an anode, means applyingpositive potentials to the screen grid and anode relative to thecathode, and means including resistive output impedance connected to theanode for maintaining the said potential of the anode less positive thanthat of the screen grid, said tube having a positive effective internalresistance for voltage changes impressed between the control grid andthe cathode.

13. In combination: a multi-electrode electron discharge tube having acathode, a control grid, a screen grid and an anode; a connection fromthe 'cathodeto the anode, said connection containing a direct currentvoltage source joined at its nega.- tive terminal to the cathode, and aresistive output impedance having a terminal joined to the anode; and aconnection from the screen grid to a, point on the cathode-to-anodeconnection such as to maintain the screen grid at a more positivepotential than the anode, relative to the cathode.

14. In combination: a multi-electrode electron 10 discharge tube havinga cathode, a control grid, a

screen grid and an anode, a connection from the cathode to the screengrid, said connection containing a direct current voltage source forapplying a. positive potential to the screen grid relative to thecathode, a connection from the screen grid to the anode, said connectioncontaining a resistive output impedance.

JOSEPH MASSOLLE.

HANS VOGT.

JOSEF ENGL.

